Tumor cells often retain the capacity for differentiation and maturation into non-replicating terminal cells. The purpose of this project is to characterize the sequence of changes which occur in malignant melanocytes as they differentiate, mature, and die, and to explore the possibility that the rate at which this process occurs is a function of an intrinsic cyclic nucleotide dependent, intracellular regulatory mechanism. BIBLIOGRAPHIC REFERENCES: Kreider, J.W., Wade, D., Rosenthal, M. and Densley, T. Maturation and Differentiation of B16 Melanoma Cells Induced by Theophylline Treatment. J. Natl. Cancer Inst. 54:1457-1467, 1975. Banks, J., Kreider, J.W. Bhavanadan, V.P. and Davidson, E.A. Anionic Polysaccharide Production and Tyrosinase Activation in Cancer Research 36: 424-431, 1976.